Population aspects of pit vipers, Craspedocaphalus travancoricus, Craspedocaphalus peltopelor and Hypnale hypnale, were studied in the southernmost Western Ghats of Tamil Nadu, India, comprising Kalakad Mundanthurai Tiger Reserve and the contiguous Courtallam range, covering an area of 1000 sq km. The information gained from marked pit vipers provides the core of this study and is the main basis for conclusions regarding population size, structure, activity, home range and movements. The high population size and small home range of these ambush hunters, with abundant prey base in this area, reveal a suitable habitat in a moderately undisturbed tropical forest.